1. Field of the Invention
The present invention is related to the field of liquid measurement systems. More specifically, the invention relates to a real-time mass flow measurement system that measures fuel mass delivered per stroke of an injection pump or a fuel injector.
2. Description of Related Art
Accurate measuring capabilities of flow measurement systems have become very important in the automotive industries where increasingly demanding emission and fuel economy regulations require strict control of the amount of fuel delivered to the engine cylinders from, for example, injection pumps and fuel injectors. For example, because of these increasingly demanding emissions and fuel economy regulations, the metering capabilities of the modern fuel injection systems in diesel engines have improved significantly and recent fuel injection systems deliver fuel to each cylinder with a maximum volume variation of 1-2%. Due to this narrow tolerance, the measurement systems must be capable of measuring fuel delivery with an accuracy of 0.2-0.4% to provide reliable and meaningful information regarding the amount of fuel injected. To provide flexibility and additional utility, these measurement systems should also be able to measure both the average amount of fuel delivered, and the amount delivered in a single stroke (xe2x80x9cshotxe2x80x9d) or multiple strokes of a fuel injector or injection pump plunger or piston.
Of course, various flow measurement systems are generally known in the art and a number of measurement systems have been developed for measuring fuel delivered to internal combustion engines. Many of the simple systems require volumetric measurement of the fluid which is sensitive to fluid expansion and contraction caused by temperature variations. Therefore, these volumetrically based measurement systems are generally not sufficiently accurate enough to be used to precisely monitor the amount of fuel delivered by a fuel injector or an injection pump.
Other measurement systems measure mass flow by using a precision balance to measure mass of the fluid. Although these systems provide accurate measurements with minimal sensitivity to temperature, these balance systems are time consuming to use and sensitive to environmental vibrations. Therefore, these precision balance systems are not easily adaptable to industrial environments such as manufacturing facilities where engines are assembled and tested for proper operation.
Another type of mass flow measurement system uses a precision bore tube and a pressure transducer to obtain accurate mass measurements of the fluid. An example of such a mass flow measurement system is shown in U.S. Pat. No. 3,835,700 to Gamble which discloses a fuel meter system that continuously measures the total flow to the engine by using a precision bore tube and a pressure transducer to measure the pressure of the column height to establish the mass flow of the liquid. One limitation of Gamble""s system is that it only provides an average fueling measurement to the engine and does not provide any means to accurately measure the mass flow provided to each cylinder of a multi-cylinder engine.
U.S. Pat. No. 4,088,012 to Emerson discloses a fuel injection metering system wherein the engine fuel injection system is connected to a metering apparatus comprising transparent graduates. Each engine cylinder is provided with a corresponding transparent graduate which captures the fuel delivered by the injector. Emerson""s system, however, is a very simple system that requires visual readings of the fuel level in the respective graduates which is highly inaccurate and will not provide the degree of accuracy required to test modern fuel systems.
U.S. Pat. No. 4,171,638 to Coman discloses another system for measuring pulsating fluid flow wherein the discharged fluid is collected in a container for a predetermined number of flow pulses, the volume or the weight of the fuel is measured by a transducer, and the data processed to determine the amount of fluid collected for a predetermined number of fluid flow pulses. The ""638 patent, however, discloses a measurement system applicable for a single cylinder fuel pump and does not address the special problems encountered in measuring the mass flow provided to each cylinder of a multi-cylinder engine.
Significant difficulties arise when trying to accurately measure the mass flow provided to each cylinder of a multi-cylinder engine. Because there are multiple number of injector pumps or fuel injectors, the mass measurement event must be synchronized to the timing of the engine. In addition, the system must also be flexible enough to allow the operator to designate the injector pump or fuel injector to be measured and the number of shots measured.
Modern measurement systems have attempted to obtain such capabilities by using microprocessor based digital computers with data acquisition software programs. The use of computers and data acquisition software allowed the measurement system to measure the fuel injected by a designated injector and allowed system flexibility and friendly user interface. An example of such a system is shown in U.S. Pat. Nos. 4,453,403 and 4,714,998, both to Bussey et al. These references disclose volumetric metering equipment for a fuel injection system that uses a micro-computer to monitor and record the total volume of fuel collected and the time when each fuel injector is injecting. The system then uses the recorded data to calculate the volume of fuel collected during the time when a particular injector was injecting, thereby indirectly determining the volume of fluid injected by each injector of the multi-injector system.
However, such systems that combine fluids injected by numerous injectors and use computer software to calculate the contributions of each injector were found to be inaccurate for various reasons. The primary reason for the inaccuracy is that there is no assurance in accurately timing the injection event to the measurement data acquired for a particular injector. In theory, the computer and the data acquisition software should respond instantaneously to operate any valves needed to collect the injected fuel and record the volume of fluid collected at the precise time of the injection event. In practice, however, the inventors of the present invention found that because computers use interrupt signals through a common bus to process the data acquisition software codes, data signals and control signals, the timing of the controls for fluid collection was inconsistent. Because of the inconsistency in the time needed to process any given signal and software code, it was found that a system based on data acquisition software cannot provide consistent performance in timing the fluid collection. Thus, there was no assurance that all of the fuel injected by the designated injector is measured and recorded. In addition, these software controlled systems do not provide assurance that only full shots are collected and that the measurement in fact terminated at the end of the predetermined number of injection events. Furthermore, because the injected fluids of the numerous injectors were combined and collected together, the timing errors during the injection of one injector adversely impacted the measurements and calculations of the other injectors. Thus, it was found that a software based mass flow measurement system can not ensure measurement accuracy and certainty to the degree of precision desired.
Therefore, there exists an unfulfilled need for a mass flow measurement system that can accurately measure the fluid provided to each cylinder of a multi-cylinder internal combustion engine and ensure precise control over the timing of the mass flow measurement system.
In view of the foregoing, it is an object of the present invention to provide an improved mass flow measurement system that can accurately measure the fluid provided to each cylinder of a multi-cylinder internal combustion engine by a plurality of fuel injectors or fuel pumps.
A second object of the present invention is to provide an improved mass flow measurement system which will allow precise control over the timing of the mass flow measurement so as to synchronize the data acquisition with the pump output so as to ensure measurement accuracy and certainty.
Yet another object of the present invention is to provide a mass flow measurement system which ensures that all of the fuel delivered by a designated pump during a predetermined number of shots is captured and recorded, and at the same time, ensures that only complete shots of the fuel injector, or injection pump, plunger or piston, is captured.
In accordance with one embodiment of the present invention, these objects are obtained by an improved mass flow measurement system including a fuel measuring device with a precision bore cylinder and a pressure transducer at its base that measures fuel delivered by one of the plurality of fuel injectors or fuel pumps. The fuel measuring device also includes a connector tube that maintains fluid over the pressure transducer so as to ensure accuracy in the pressure measurement. This embodiment also includes a fuel transfer circuit for directing fuel flow to the fuel measuring device and a plurality of fuel routing devices positioned along the fuel transfer circuit for routing fuel flow from the plurality of fuel injectors or pumps into the fuel transfer circuit, each of the plurality of fuel routing devices being associated with a respective one of the plurality of fuel injectors or fuel pumps. The mass flow measurement system also includes a fuel diverter positioned along the fuel transfer circuit for diverting the routed fuel flow to either the fuel measuring device or a fuel drain and a output trigger that initiates the measurement event. The mass flow measurement system further includes a data acquisition system including a digital computer and a flow controller for controlling the fuel diverter. The digital computer includes a software program for receiving operator input data, controlling the fuel routing devices and obtaining measurement data from the fuel measuring device. The flow controller includes discrete logic components for controlling the fuel diverter thereby providing consistent timing control. A pump position sensor is also provided to allow the determination of the number of shots collected and to allow a delay time which ensures that only full shots are captured.
Also in accordance with the present invention, these objects are obtained by a method for measuring a quantity of fuel delivered by a fuel pump in a fuel system including a plurality of fuel pumps. The method includes the steps of providing a fuel measuring device for measuring fuel delivered by the fuel pump, providing a fuel transfer circuit for transferring fuel flow from the plurality of fuel pumps to the fuel measuring device, routing the fuel flow from the fuel pump into the fuel transfer circuit and diverting the routed fuel flow to either the fuel measuring device or the fuel drain. The method also includes the steps of receiving operator input data, initiating the measurement process by a trigger signal, and providing a flow controller with discrete logic components to control the fuel diverter. The method further includes the steps of providing encoder pulses which corresponds to the rotational position of the fuel pump to the flow controller, counting the encoder pulses to determine the number of shots collected and the delay time, and operating the diverter valve to divert the routed fuel flow to the fuel drain. The method also includes the steps of obtaining data from the fuel measuring device and calculating the corresponding volume of the fuel collected.
These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the invention when viewed in conjunction with the accompanying drawings.